Show the upper limits of HP/MP

- The color is `map (/ 2) color`.
- Does Monitor class have too many variables?
Fix a bug for destroyed bodies

- I didn't know the fact that DestroyBody() frees the memory. This makes
  swig python-objects dangling pointers.
- This fix is much temporary. I'll improve.
Restruct Entity

- Add BodyData and FixtureData for userData for userData instead of
  dict.
- Simplify Entity class. Create* method is moved to
  Entity.game.world.Create*.
- Use Event class.
Add bound to Plyaer.walk/jump

- The range is [-1, 1].